Underwater Target Estimation Based On Wideband Laser-induced Acoustic Source

With the development of ocean economic, underwater detection area appears higher and higher application value, compared to the microwave method, acoustic method has lower loss for the underwater transmission, thus lead to a result of longer detection range. However, the traditional method used sonar for underwater acoustic detection has certain limitations, like low measurement efficiency, limited survey range, unable to work in danger area like reef cluster. As a new type of wide-band acoustic source, laser-induced acoustic source can emit high power laser pulse in the aerial platform remotely, by converting the optical energy into an acoustic pressure wave in the water surface through optical breakdown, propagate as acoustic signal in the water, and can use the airbone receive method to detect the signal reflected by the target. Laser-induced acoustic source not only has excellent characteristics like high power, narrow pulse in time domain, wide-band spectra in frequency domain, but also has high measurement efficiency, can take the task in the hostile environment, thus this is a acoustic source with large potential application value;At the beginning of this paper, we briefly introduced the developed history and advantages of laser-induced acoustic, compared with the traditional underwater detection methods. Then in-troduced some theoretical analysis of the laser-induced acoustic source; For such a quick-decay transient signal, traditional spectra estimation method was unable to achieve high frequency reso-lution, so this paper proposed a spectra estimation method using Prony’s algorithm to decomposed the transient into a series of damped sinusoidal components, in the paper introduced the relevant theory and derivation of AR spectra estimation, and analysis the pros and cons of difference solu-tions, finally introduced several ways to improve the performance of Prony’s algorithm.Since the propagation model of acoustic signal transmit underwater is very complex, and the reflect model was influenced by the parameters like material, size or shape of the target, so this paper used the Finite Element Method software COMSOL to conduct the statics simulation and transient simulation for the acoustic-solid interaction; In the static simulation calculated the target reflect characteristic for the spherical wave, through theoretical analysis to verified of the simulation result, then proposed a method to achieve the material thickness estimation through a single wideband acoustic pulse, and verify its effectiveness with simulation result. Within the transient simulation analysis the interact progress of Gauss point acoustic source and reflect target, utilized the Prony’s algorithm to estimate the spectra of incident signal and reflect signal, in order to realize the thickness estimation, verify the feasibility of the proposed method for the transient signal, used the acoustic scattering model and deconvolution algorithm to made a simple estimation of the size of the target, and verified it with the transient simulation result.At the end of this paper, we conducted the relevant verity experiment in an anechoic pool, estimate the thickness of the perspex and rubber, the result is very close to the real ones with an error of only3.08%for perspex and5.12%for rubber; At the end of the article, gave the correspond explanation of the error. And conducted the size estimation of the underwater rock region on the ship in the Qiandao Lake, collected the data and make the relevant calculation and analysis.